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Soluble Fiber Simplified

Soluble fiber is a key factor of metabolic health. Unfortunately, it has been thrown to the wayside recently with the re-emergence of low-carb diet trends such as the Paleo Diet. But beware: its absence has a number of adverse effects.

By definition, fiber is a non-digestible food component with physiological effects on humans. (1) These physiological effects are beneficial to our bodies and range from optimal metabolism to healthy bacteria. InsideTracker recommends food with soluble fiber for a variety of biomarkers, most importantly the regulation of cholesterol and glucose. My aim in this article is to explain why.

Insoluble Versus Soluble

There are two types of fiber: soluble and insoluble. (2) Insoluble fiber is the form most commonly found in vegetables. Celery strings and kale stems are good examples. Its primary purpose is to create “matter” or “content” to move through our digestive systems—if you get my gist. While it’s incredibly important for a multitude of reasons to eat a variety of fruits and vegetables, insoluble fiber from just vegetables is not enough for maximal health. IT’S NOT ENOUGH!

How do we get enough? Eat both insoluble and soluble fiber. Soluble fiber is named for its ability to dissolve in water, or absorb it. As it moves through the GI tract, it begins to swell and skims the lining of your intestines—resulting in an effective intestinal cleansing.

Soluble fiber is found in oatmeal, lentils, beans, nuts, flaxseed, and psyllium, to name a few examples. It is also found in fruits high in pectin, such as apples, citrus, and berries. (3) Whole grains also provide soluble fiber, but they aren’t enough to meet your body’s needs. They are, however, packed with vitamins and minerals that are stripped away in processing to make “white” grain products. (4)

Back to the Car

Think of soluble fiber as a physical “car” that picks up “passengers” and transports them out of your body. Insoluble fiber is the “gas” that powers the car. Without the physical car, the insoluble fiber in all those vegetables you’ve worked so hard to incorporate into your diet can’t reach its full fibrous potential.

Linking to Cholesterol

One of soluble fiber’s most frequent passengers on its journey out of the body is bile, a digestive juice necessary for fat breakdown. Bile is made from cholesterol and therefore reduces total cholesterol when it passes out of the body. That’s because the liver has to make it again from other cholesterol—ultimately resulting in less cholesterol in circulation in your body. (5) Soluble fiber is one of the few natural ways to boost this process. In fact, a specific type of cholesterol-lowering medication, called bile acid resins, is designed after this principle.

What about Glucose?

Soluble fiber also helps to lower blood glucose. (6) It increases the thickness of food in the stomach, which causes food to be digested more slowly. This results in smaller peaks – and subsequent valleys – in blood glucose levels. It also results in less glucose being absorbed into the blood. The thick, soluble fiber does not mix as well with stomach juices necessary for digestion, allowing some glucose to pass without being digested. (7)

Don’t Fear the Fiber

In addition to the effects on cholesterol and glucose, soluble fiber aids in appetite control. It makes us feel fuller (even when caloric intake is the same) and prolongs those feelings of fullness, often resulting in less food intake throughout the day and thereby making it an excellent weight management tool. (6)

One study examined the difference in weight loss between a conventional weight loss intervention—providing advice on portions, healthy eating, exercise, and so forth—versus simply encouraging people to incorporate more fiber. Those who ate more fiber still lost a significant amount of weight, without the stress of multiple habit changes. (7) If it is difficult for you to stick to a lot of changes that seem typical for weight loss regimens, start by simply increasing fiber—both soluble and insoluble.

A Time and a Place for Low-fiber Foods

After a hard workout, your muscles need to restore their glycogen stores. Glycogen is essentially a stored carb our muscles use to sustain prolonged activity. The ideal post-workout recovery food intake is a mixture of carbs AND protein—not just protein. (8) If you are hesitant about adding carbs to your diet, incorporate quickly digestible carbs around your workout to start. Fruit, white potatoes, and rice are great whole-food options in addition to specifically formulated sports products.

If you are exercising for over an hour, your body may need nourishment during the workout. But you have to be truthful with yourself about your intensity level. Not all workouts require a glycogen recovery effort. A leisurely hour walk and a strenuous hour run have completely different refueling requirements.

Hierarchy of Fiber

While all soluble fiber is good for us, a specific classification takes the (whole grain) cake on promoting healthy cholesterol and glucose: viscous soluble fibers. (9) Viscous soluble fibers form a gel when eaten, which turns the car in our analogy into a minivan. Two types in particular work great: β-glucan and psyllium husk. (10, 11) Those may sound like foreign substances but β-glucan is primarily found in oats and psyllium husk can be bought at most health food stores (it’s also the primary fiber in Metamucil).

If I told you that adding one thing to your diet could reduce your cholesterol fasting glucose, tame your appetite, and help with weight control you would sign on the dotted line, right? The answer isn't a so-called “superfood” or magic pill. It’s just oats. They can easily be incorporated into your routine each morning as a bowl of oatmeal. Short on time? Throw them in a smoothie. Psyllium husk can also easily be added to any smoothie, sauce, or baked goods to boost the soluble fiber content.

Recap of soluble fiber and health

Eat soluble fiber!

Don’t be afraid of carbohydrates—that's where soluble fiber is found

Soluble fiber can help to lower your cholesterol and glucose

Soluble fiber promotes weight loss and maintenance

Consume oats and psyllium husk for high concentrations of soluble fiber

InsideTracker monitors cholesterol and fasting blood glucose, as well as over 25 other biomarkers. Our recommendations, including foods that contain soluble fiber, are designed to optimize your biomarkers and overall health. We also consider your age, gender, ethnicity, and activity level to make the best suggestions.

See if soluble fiber can improve your health and find out what other foods will help. Fiber is just one health-improving vehicle InsideTracker can recommend. There are many more suited for your biochemistry. Take the guesswork out of your food selection. We’ve done the research for you.

(1) American Association of Cereal Chemists. The definition of dietary fiber: report of the Dietary Fiber Definition Committee to the Board of Directors of the American Association of Cereal Chemists. Cereal Foods World. 2001; 46:112–126.